Patent GB-1222146-A (GB)
Title: Improvements in or relating to fluidic speed sensors
Inventor: LEATHERS JOHN WILLIAM
IPC: F15C1/00
Filed: 1968-07-01
Abstract: 1,222,146. Speedometers. PLESSEY TELECOMMUNICATIONS RESEARCH Ltd. June 27, 1969 [July 1, 1968; April 15, 1968], Nos. 31329/68 and 19188/69. Heading G1K. [Also in Division G3] A fluidic device for sensing the speed of a moving body 24 with an operating surface comprises a nozzle 28 arranged to direct a jet 30 of fluid into the boundary layer of the operating surface in a direction having a component perpendicular to the direction of movement of the body 24 past the nozzle 28 and a component parallel to the operating surface and a collector disposed confronting the nozzle, the operating surface being so shaped that its disposition relative to the nozzle 28 is unaffected by the movement of the body and the boundary layer being defined as the layer of fluid adjacent a solid body in which movement in the same direction is caused by movement of the body. The proportion of the jet of fluid received by the collector is a maximum when the body is stationary if the collector is displaced from the nozzle solely in the direction of issue of the jet and at a predetermined speed if its displacement from the nozzle has a suitable component in the direction of movement of the body. Two collectors 32,34 may be so disposed each side of the jet 30 when the body is moving at a predetermined speed that a change in speed causes an increase in pressure at one collector and a decrease at the other and a fluidic momentum-interaction device 36 may give an output at a port 38 when the pressures are equal, otherwise fluid may escape from one or other of vents 40, 42. In any arrangement there is an optimum distance between nozzle and collector for greatest sensitivity. Sensitivity increases with the effective thickness of the boundary layer, the optimum being reached when the jet is completely enveloped. The effective thickness can be increased by roughening the surface. Sensitivity can also be increased by providing confronting operating surfaces. In the embodiment of Fig. 5 (not shown) two spaced parallel shafts coupled by a pair of idler gears rotate in opposite directions so that the two curved operating surfaces move in the same direction with the nozzle arranged to direct the jet therebetween. In the embodiment of Fig. 8 inner and outer pairs of operating surfaces are formed by confronting, annular lips 96, 98 and 97, 99 of two discs 90, 92 secured on a shaft 94 and forming an inner annular cavity 100 inwhich a nozzle 106 is disposed, directing a jet through a gap into an outer annular cavity 109, into which project a pair of collectors 108. In Figs. 6, 7 (not shown) the outer lips and cavity are omitted and in Fig. 9 (not shown) one of the discs (in either of the last two embodiments) is free to rotate on a stationary shaft along the axis of which supply pipe for the nozzle is located to avoid interference with the boundary layers, the two discs being magnetically coupled for rotation. It is also stated that when two collectors are provided, the output may take the form of a differential output signal instead of a momentum device.